1. Field of the Invention
The present invention relates to an air cushion having a support pin structure for absorbing shock, a method for manufacturing the air cushion, and footgear comprising the air cushion.
More particularly, the present invention relates to an air cushion having a support pin structure for absorbing shock, a method for manufacturing the air cushion, and footgear comprising the air cushion which do not exhibit any bulging effect, even upon application of an external pressure, to thereby improve the stability thereof.
2. Discussion of Related Art
As well known, feet of a human being have some functions of supporting his or her body weight by the contact onto the ground upon an upright position and executing walking or exercise with an appropriate movement. Mostly, the sole of a normal foot is in contact with the ground except for a vaulted portion thereof, upon the upright position, to thereby take a stable upright position. In addition, the vaulted portion of the sole of foot is extracted like a spring, upon walking or running, to thereby absorb the shock applied onto the foot. Moreover, the vaulted portion of the sole of foot makes the front portion of the foot comprised of toes in a free-movement state, to thereby execute a light and smooth walking or running. It is therefore desirable to select footgear which allows the sole of foot to be in contact with the ground to thereby distribute the load applied thereto.
For instance, generally, during a sportsman takes exercise such as running, basketball, football, tennis and the like, a great amount of shock is applied onto his foot in a continuous and repetitive manner and, whenever the foot is in contact into the ground, is directly transmitted to the foot. At this time, his foot during the exercise can absorb the shock applied, while supporting his body weight, but since the amount of the shock applied corresponds to several times as much as his body weight, the cartilaginous portion of the foot is likely to be weakened, which will be easily exposed to damage or aging.
Therefore, it is very important for a sportsman or a general person to select footgear which can completely absorb an amount of shock applied.
For this end, various kinds of conventional cushions for absorbing the shock are mounted in the footgear, specifically sports shoes.
The footgear inclusive of the sports shoes is comprised of a sole having a laminated form of an outsole, a midsole and an insole, and an outer surface attached on the sole to surround the foot. In this case, a shock absorbing material is typically disposed on the sole of the footgear.
By way of example, a conventional cushion for shock-absorbing in an initial developing step is made of a general elastic material such as, for example, rubber, sponge, polyurethane foam, etc. In more detail, the elastic material is processed to a plate shape and attached between the outsole and the midsole or between the midsole and the insole, such that it can absorb the shock applied to the sole of foot, while supporting the sole of foot. However, the conventional air cushion fails to completely absorb the large amount of shock corresponding to hundreds of kilograms to tens of tons. Unfortunately, moreover, upon the application of a tremendous amount of shock the cushion is under a permanently deformed state, which does not exert any absorbing performance.
On the other hand, another shock absorbing material has been developed, in which a flow type material in a liquid or semi-solid type (i.e., gel) is enveloped in a sealing body made of an elastic material. However, since most of the flow type material is incompressible, it fails to completely absorb the shock applied onto the shock absorbing body in the same manner as the above.
Recently, an air cushion as a shock-absorbing material is developed and widely used in sports shoes, etc.
The sports shoe having a conventional air cushion is shown in FIGS. 1 and 2. The air cushion is comprised of an upper plate 11, a lower plate 12, and a side plate 13. In this case, the upper and lower plates 11 and 12 are made of a flexible material and separated at a predetermined interval to be faced in parallel to each other. The side plate 13 is made of the same flexible material and is melting-attached to the upper plate 11 to maintain the air-tightness along the edge of the upper plate 11, at the top portion thereof. At this time, the melting attachment utilizes a conventional method such as an ultrasonic melting. Under the above construction, the sealing of the upper plate 11, the lower plate 12, and the side plate 13 forms a cavity in the interior thereof, into which air for shock-absorbing fills to exert the shock absorbing performance, whenever a predetermined shock is applied to the air cushion. As shown in FIGS. 1 and 2, the air cushion is secured on an outsole 2, and an outer surface 3 is attached on the outsole 2, such that in the shoe where the foot is received by means of the outer surface 3, the air cushion is disposed in the midsole on the rear portion of the shoe, that is, the direct lower portions of the sole of foot and the heel of the foot. The air filling the interior of the air cushion is compressed, such that it can fully absorb and buffer the shock force generated when the load of the user of the shoe is applied to the lower side. In this case, during the user of the shoe takes the exercise, the amount of shock generated due to the load of the user's body weight is transmitted to the shoe, whenever the shoe is in contact with the ground. Generally, as the amount of shock is primarily collected to the heel of the shoe and is then moved to the front portion of the shoe, the pressure of air is applied even to the front portion thereof. The shock force applied to the shoe is buffered by the buffering action through the air compression in the air cushion. At this time, if the shock is applied to a part of the upper plate 11, the part of the upper plate 11 (hereinafter, referred to simply `a compressed portion`) is pushed and compressed, to thereby execute a primary buffering performance. Concurrently, however, the interval between the upper plate 11 and the lower plate 12 is reduced on the compressed portion, and the air is collected on the portion (hereinafter, referred to simply `an non-compressed portion`) where no push or compression is generated, to thereby form a strong air pressure. Thereby, the formation of air pressure causes the non-compressed portion to be expanded. Hereinafter, this phenomenon refers to `a bulging effect` in this specification. In case of such the conventional air cushion, there is a problem that a bulging effect is exhibited whenever shock is applied, as shown in FIG. 3. As a result, when the upper plate 11 and the lower plate 12 on the non-compressed portion expanded due to the bulging effect are restored in their original positions, they are likely to momentarily fail to be in the position of their original height due to the inertial force, which results in the formation of a curved surface. This bulging effect continues until the air pressure due to the shock force is somewhat removed, that is, the shock force cannot further deforms the upper plate 11, the lower plate 12 and the side plate 13. Moreover, since the bulging effect occurs on the several portions of the air cushion in continuous and repetitive manners all the time during the user takes the exercise, the curved surface is continuously generated, deformed and removed, in the state where the upper and lower plates 11 and 12 of the air cushion do not maintain the flat surface. However, there still occur problems that the conventional air cushion does not exert an excellent shock-absorbing performance and gives somewhat inconvenience to the user upon wearing.
Also, there has been recently developed an air cushion having a support thread structure between the upper and lower plates 11 and 12 to reduce the bulging effect, as shown in FIGS. 4 and 5. In construction, the support thread 14 is adapted to connect the upper and lower plates 11 and 12, as shown in FIGS. 6 and 7. When the upper and lower plates 11 and 12 are woven into a plain fabric where the warp and woof threads are woven, the support thread 14 becomes a loop thread for the warp threads for weaving the upper and lower plates 11 and 12, such that it secures the upper and lower plates 11 and 12 against each other, while maintaining an air chamber having a predetermined interval between the woven upper and lower plates 11 and 12. At this time, the support thread 14 is comprised of a typical synthetic fiber or a metal wire. The upper and lower plates 11 and 12 are woven into double fabrics and are secured to each other by means of the side plate 13. Furthermore, the upper and lower plates 11 and 12 form a coating layer on the outer surface thereof to thereby maintain the air-tightness therebetween. Otherwise, the upper and lower plates 11 and 12 are closely attached and secured on the inner side of a cushion body 23 constituting the side plate 13. The cushion body 23 is formed by a thermoplastic polyurethane which is adequate to maintain the air-tightness therein, thereby preventing controlling the discharge of air filling in the interior thereof.
Therefore, the compression is formed by the curving of the support thread 14 on the compressed portion of the upper plate 11, but the expansion is not formed over the length in a height direction of the support thread 14 on the non-compressed portion thereof, unless the support thread 14 is cut. As a result, the support thread 14 functions to suppress the formation of the curved surfaces on the upper and lower plates 11 and 12. But since the support thread 14 is woven into the loop fabric, the height of the support thread 14 is not adaptively controlled. Therefore, there occurs a problem that all of the upper and lower plates 11 and 12 have a flat structure. This is because the formation of support thread 14 is dependent upon a weaving manner. However, the air cushion having the flat structure is not well matched with the sole of foot having the curved surface, such that it is covered not over the whole sole of foot, but only on a predetermined portion thereof. Therefore, there occurs a problem that the air cushion does not exhibit a complete shock absorbing performance over the whole sole of foot. As the sole of foot takes a three-dimensional shape, the air cushion constructed as the above fails to provide a satisfied buffering effect and a convenient wearing feeling to the user. Hence, there is a need to develop a novel air cushion for completely absorbing shock.